How do i know if my ankle is sprain or broken?

Can't walk if broken: You can still walk on a sprained ankle, although it may be very swollen and even feel unstable if the sprain is severe. A sprain means that you have torn ligament fibers. With a broken (fractured) ankle the bones are unstable. The sharp, broken edges pull on the sensitive tissues surrounding the bone and cause extreme pain. With this combination it is usually too painful to stand, much less walk.

Sprain vs break: Usually, if the ankle is broken, you would not be able to walk on it or you would have severe pain doing so. The best way to know is by getting an xray.